[vtkusers] Visualisation non linear cells

[Soeren Gebbert]

Hi Jhon,
thank you for your answer,
i just implement a 9 node biquadratic quad, a 27 node triquadratic 
hexahedron,  a 6 node quadratic-linear quad
and a 12 node quadratic-linear wedge in VTK 4.5.
I think i dont want to improve the triangulation system to add new 
nodes, i just take care that the contour
algorithm is geometric conform to the triangulation (looks nicer). With 
these new types i dont need
Subdivide() to add temporary points for clipping and contouring :D. 
Maybe my companie allows my to
contribute this code ... .

I took a look at vtkGenericCellTessellator and i hope to use this 
helperclass to create curved surfaces.

Best Regards
soeren

John Platt wrote:

>Hi Soeren,
>
>I am no expert in VTK but I have used nonlinear cells and also wish to
>extend the types available. These are some comments based on what I have
>seen in the code rather than experience implementing a new cell type.
>
>Triangulate() is used by surface filters (vtkDataSetSurfaceFilter) to
>replace quadratic faces by linear triangles. The schemes are carefully
>chosen so as NOT to introduce new points. Implementing a new scheme with
>more points to give better resolution of curved edges will require some
>care to ensure adjacent edges detect the new points. The point data must
>also be interpolated. It may also be necessary to make Subdivide()
>compatible with Triangulate().
>
>In version 4.4 there does not appear to be any concrete implementations
>of Tesselate(). Have you looked at?
>
>http://www.vtk.org/doc/nightly/html/classvtkGenericCellTessellator.html
>
>HTH
>
>John.
>
>-----Original Message-----
>From: vtkusers-bounces at vtk.org [mailto:vtkusers-bounces at vtk.org] On
>Behalf Of Soeren Gebbert
>Sent: 13 January 2005 15:40
>To: vtkusers at vtk.org
>Subject: [vtkusers] Visualisation non linear cells
>
>Dear vtkusers and developers,
>I'm using vtk 4.4 and paraview 1.8.2 at linux and windows. I'm a
>beginner
>in vtk but i have some important questions to ask:
>
>I want to add new nonlinear celltypes to vtk, like a quadratic quad with
>an area center point and so on.
>And i want to visualize them with a curved surface. Since now i used
>paraview to visualize
>the already implemented quadratic celltypes (QuadraticTetra ...). In
>paraview i used the TempTessellatorFilter to get
>a proper visualisation. I thought this filter is also implementet in vtk
>but it isnt. So i searched for a
>proper functionality in vtk to get my curved surface, but i didnt found
>a filter.
>
>As it is described in the vtk books, the quadratic cells will be
>visualized as linear cells.
>I guess the reimplemented function "Triangulate" from vtkCell in the in
>the vtkNonLineareCell classes is doing this.
>But there is a virtual function named Tesselate declrated in
>vtkNonLinearCell, i guess this function will be used to render curved
>surfaces, but this function is not implemented yet. So my question is:
>
>1.) Is the function "Triangulate" responsible for the visualisation of
>the different celltypes in vtk?
>2.) If 1. is ture, can i reimplement the Triangulate function to create
>curved surfaces for nonlineare cells?
>3.) Is it possible to reimplement the "Tesselate" function and use this
>for visualisation of nonlinear cells?
>4.) If 1. - 3. is not true, what can i do to visualize 2D and 3D
>nonlinear cells to get the form that is described
>     in the shape function of these cells?
>
>Thanks alot and best regards
>Soeren Gebbert
>
>btw.:
>Please excuse my english.
>
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